The present invention relates to an apparatus for removing and/or placing a workpiece from or in an injection mold of an injection molding machine, in particular injection molding machine for processing plastics.
Injection-molded articles have to be removed cyclically from the open injection molding machine, before a next injection-molding step can begin. German patent publication no. DE 199 39 228 describes an extraction unit having a globoid cam gear which is controlled as a consequence of a relative movement between the fixed and moving platens to thereby operate a swingable lever with attached gripping mechanism. The globoid cam gear is hereby supported upon the moving platen and driven by a toothed rack which is connected to the fixed platen.
This type of extraction unit suffers shortcomings because the toothed rack continues to operate the globoid cam gear, when the mold opens beyond a preset stroke during normal operation, so that the swingable lever assumes an undesired position. In the event, the mold opens even further, there is the risk of disengagement of the toothed rack from the spur gear that is seated on the output shaft of the globoid cam gear and detachment of the bearing of the toothed rack upon the cam gear.
Excessive opening strokes of platens are oftentimes caused during operation of an injection molding machine because the control of the clamping mechanism may become defective, or because necessary maintenance works or mold exchange needs to be done. If the injection molding machine should be returned to the normal operating state, after undergoing such an excessive opening, care must be taken to precisely fit the engagement between the toothed rack and the globoid cam gear and to precisely set the operating point of the globoid cam gear in order to accurately match the movement of the swingable lever.
It would therefore be desirable and advantageous to provide an improved apparatus for removing and/or placing a workpiece from or in an injection mold of an injection molding machine, to obviate prior art shortcomings and to operate in a reliable manner, even when a predefined end position of the opening stroke is exceeded.